Heretofore x-rays have been produced using high voltage tubes where electrons impinge upon metal anodes. These tubes are relatively inefficient, require high voltages, and vacuum tubes for ballistic electron transport. The low intensity capable by this technology and the minimum energy capable of passing through the necessary windows from the vacuum tube to room pressure make these tubes incapable of meeting current technological needs for bright and soft x-ray sources such as x-ray lithography.
Synchrotrons have been proposed and are now being used on a research basis for x-ray lithography. The huge size, weight, cost and complicated nature of synchrotrons are severe disadvantages for use of these machines for x-ray lithography.
A newer source for soft x-ray is the laser induced plasma source. In this type of machine an intense laser pulse incident upon a solid target material creates a dense plasma from the target material, destroying it. The plasma generates an x-ray pulse.